Accuracy of Intercepting Moving Tactile Targets

Motion perception in touch: resolving contradictory findings by varying probabilities of different trial types

Representational momentum describes the typical overestimation of the final location of a moving stimulus in the direction of stimulus motion. While systematically observed in different sensory modalities, especially vision and audition, in touch, empirical findings indicate a mixed pattern of results, with some published studies suggesting the existence of the phenomenon, while others do not. In the present study, one possible moderating variable, the relative probabilities of different trial types, was explored in an attempt to resolve the seemingly contradictory findings in the literature. In some studies, only consistently moving target stimuli were presented and no representational momentum was observed, while other studies have included inconsistently moving target stimuli in the same experimental block, and observed representational momentum. Therefore, the present study was designed to systematically compare the localization of consistent target motion stimuli across two experimental blocks, for which either only consistent motion trials were presented, or else mixed with inconsistent target motion trials. The results indicate a strong influence of variations in the probability of different trial types on the occurrence of representational momentum. That is, representational momentum only occurred when both trial types (inconsistent and consistent target motion) were presented within one experimental block. The results are discussed in light of recent theoretical advancements in the literature, namely the speed prior account of motion perception.

Multisensory integration reduces landmark distortions for tactile but not visual targets

Target localization is influenced by the presence of additionally presented nontargets, termed landmarks. In both the visual and tactile modality, these landmarks led to systematic distortions of target localizations often resulting in a shift toward the landmark. This shift has been attributed to averaging the spatial memory of both stimuli. Crucially, everyday experiences often rely on multiple modalities, and multisensory research suggests that inputs from different senses are optimally integrated, not averaged, for accurate perception, resulting in more reliable perception of cross-modal compared with uni-modal stimuli. As this could also lead to a reduced influence of the landmark, we wanted to test whether landmark distortions would be reduced when presented in a different modality or whether landmark distortions were unaffected by the modalities presented. In two experiments (each n = 30) tactile or visual targets were paired with tactile or visual landmarks. Experiment 1 showed that targets were less shifted toward landmarks from the different than the same modality, which was more pronounced for tactile than for visual targets. Experiment 2 aimed to replicate this pattern with increased visual uncertainty to rule out that smaller localization shifts of visual targets due to low uncertainty had led to the results. Still, landmark modality influenced localization shifts for tactile but not visual targets. The data pattern for tactile targets is not in line with memory averaging but seems to reflect the effects of multisensory integration, whereas visual targets were less prone to landmark distortions and do not appear to benefit from multisensory integration.NEW & NOTEWORTHY In the present study, we directly tested the predictions of two different accounts, namely, spatial memory averaging and multisensory integration, concerning the degree of landmark distortions of targets across modalities. We showed that landmark distortions were reduced across modalities compared to distortions within modalities, which is in line with multisensory integration. Crucially, this pattern was more pronounced for tactile than for visual targets.

Tapping on a target: dealing with uncertainty about its position and motion

Reaching movements are guided by estimates of the target object's location. Since the precision of instantaneous estimates is limited, one might accumulate visual information over time. However, if the object is not stationary, accumulating information can bias the estimate. How do people deal with this trade-off between improving precision and reducing the bias? To find out, we asked participants to tap on targets. The targets were stationary or moving, with jitter added to their positions. By analysing the response to the jitter, we show that people continuously use the latest available information about the target's position. When the target is moving, they combine this instantaneous target position with an extrapolation based on the target's average velocity during the last several hundred milliseconds. This strategy leads to a bias if the target's velocity changes systematically. Having people tap on accelerating targets showed that the bias that results from ignoring systematic changes in velocity is removed by compensating for endpoint errors if such errors are consistent across trials. We conclude that combining simple continuous updating of visual information with the low-pass filter characteristics of muscles, and adjusting movements to compensate for errors made in previous trials, leads to the precise and accurate human goal-directed movements.

Tau and kappa in interception - how perceptual spatiotemporal interrelations affect movements

Batting and catching are real-life examples of interception. Due to latencies between the processing of sensory input and the corresponding motor response, successful interception requires accurate spatiotemporal prediction. However, spatiotemporal predictions can be subject to bias. For instance, the more spatially distant two sequentially presented objects are, the longer the interval between their presentations is perceived (kappa effect) and vice versa (tau effect). In this study, we deployed these phenomena to test in two sensory modalities whether temporal representations depend asymmetrically on spatial representations, or whether both are symmetrically interrelated. We adapted the tau and kappa paradigms to an interception task by presenting four stimuli (visually or auditorily) one after another on four locations, from left to right, with constant spatial and temporal intervals in between. In two experiments, participants were asked to touch the screen where and when they predicted a fifth stimulus to appear. In Exp. 2, additional predictive gaze measures were examined. Across experiments, auditory but not visual stimuli produced a tau effect for interception, supporting the idea that the relationship between space and time is moderated by the sensory modality. Results did not reveal classical auditory or visual kappa effects and no visual tau effects. Gaze data in Exp. 2 showed that the (spatial) gaze orientation depended on temporal intervals while the timing of fixations was modulated by spatial intervals, thereby indicating tau and kappa effects across modalities. Together, the results suggest that sensory modality plays an important role in spatiotemporal predictions in interception.

A Novel Wearable and Wireless Device to Investigate Perception in Interactive Scenarios

The aim of the present work is to introduce a novel wearable device suitable to be used to investigate perception in interactive tasks, on individuals with and without sensory disabilities. The system is composed by small units embedded with sensors and actuators that allows emitting different kind of stimuli (light, haptic, sound) and to record the user response, thanks to a capacitive sensor. We validated the system by implementing an interception task in three different sensory modalities: visual, tactile and auditory. Six subjects with normal sight were asked to tap either a static or a moving stimulus generated by 6 units placed on their forearm. Results suggest that the system can effectively provide new insights in characterizing how perception principles vary when perceptual judgement occurs through different senses. This confirms the device potential in contributing to the design of rehabilitation protocols rooted on neuroscientific findings, for people with sensory impairments.